The present invention relates to a lip-like seal for creating liquid-tight sealing between a fluid pressure slid (operated) piston body and a piston sliding wall.
A lip-like seal is known in the art. The lip-like seal has a lip portion. The lip portion diagonally extends from an outer peripheral portion of an end of a piston body on the fluid pressure applied side towards a piston sliding wall. For example, there is shown in Japanese Utility Model Registration Publication Gazette No. 1-34744 and in Japanese Utility Model Application Laying Open Gazette No. 1-69973 such a lip-like seal.
For the case of conventional lip-like seals, a lip portion a is merely arranged to extend towards a piston sliding wall b, as shown in FIG. 9. The problem with such arrangement is that the fitting of a piston body c into a bore d results in producing an unwanted distribution of contact reaction force occurring between the lip portion a and the piston sliding wall b. As shown more specifically in FIG. 10, the resulting distribution is a bell-shaped or a single-peaked distribution having only one peak value p. Such single-peaked distribution has the drawback that a drop in lip portion durability and the occurrence of various damage or the like to lip portions may directly lead to deterioration in sealing action.
Bearing in mind the above-described problems with the prior art sealing techniques, the present invention was made. It is therefore a general object of this invention to improve the action of sealing without causing a drop in lip portion durability.